tests: Add a migration test with many clients connecting in two waves

tests/acceptance/test_write_during_migration.rb

@@ -96,19 +96,9 @@ class TestWriteDuringMigration < Test::Unit::TestCase
       dst_result = Process::waitpid2(@dst_proc)
       src_result = Process::waitpid2(@src_proc)
     end
-
   end
 
-
-  def test_write_during_migration
-
-    Dir.mktmpdir() do |tmpdir|
-      Dir.chdir( tmpdir ) do
-        make_files()
-
-        launch_servers()
-
-        src_writer = Thread.new do
+  def source_writer
     client = FlexNBD::FakeSource.new( "127.0.0.1", @source_port, "Timed out connecting" )
     offsets = Range.new(0, (@size - @write_data.size) / 4096 ).to_a
     loop do
@@ -121,10 +111,7 @@ class TestWriteDuringMigration < Test::Unit::TestCase
     end
   end
 
-        start_mirror()
-        wait_for_quit()
-        src_writer.join
-
+  def assert_both_sides_identical
     # puts `md5sum #{@source_file} #{@dest_file}`
 
     # Ensure each block matches
@@ -142,8 +129,42 @@ class TestWriteDuringMigration < Test::Unit::TestCase
       end
     end
   end
+
+  def test_write_during_migration
+    Dir.mktmpdir() do |tmpdir|
+      Dir.chdir( tmpdir ) do
+        make_files()
+
+        launch_servers()
+
+        src_writer = Thread.new { source_writer }
+
+        start_mirror()
+        wait_for_quit()
+        src_writer.join
+        assert_both_sides_identical
       end
     end
+  end
+
+  def test_many_clients_during_migration
+    Dir.mktmpdir() do |tmpdir|
+      Dir.chdir( tmpdir ) do
+        make_files()
+
+        launch_servers()
+
+        src_writers_1 = (1..5).collect { Thread.new { source_writer } }
+
+        start_mirror()
+
+        src_writers_2 = (1..5).collect { Thread.new { source_writer } }
+
+        wait_for_quit()
+        ( src_writers_1 + src_writers_2 ).each {|t| t.join }
+        assert_both_sides_identical
+      end
+    end  end
 
 
 end